Particulate matter may be incorporated into a fibrous structure for a variety of reasons. For example, chemical defense fabrics for garments for military personnel may contain vapor sorptive particles such as activated carbon. These garments typically are designed to remove poisonous gases from the air. Filters may include sorptive particles selectively to remove certain components of a liquid or gas passing through the filter. Abrasive particles may be used to create an abrasive fabric. Particulate matter may also be used in a fibrous structure to release an active agent into a fluid stream.
Eian et al. U.S. Pat. No. 4,868,032 disclosed chemical protective garments. Reinforcing bi-component fibers are needled into a meltblown web of polymer fibers onto which solid particulate matter has been dispersed. Heat is applied to bond the needled fibers to the meltblown on both sides of the fabric.
Haruvy et al. U.S. Pat. No. 4,872,220 discloses a protective clothing comprising a laminate of three layers in which one of the layers may contain an adsorptive particulate.
Giglia et al. U.S. Pat. No. 4,904,343 relates to a toxic vapor adsorptive nonwoven fabric in which activated carbon fibers and activated carbon particles may be incorporated into a web of fibrillated acrylic fiber. The fabric is prepared by the wet forming process. A slurry of the particles and fibers is deposited onto a forming belt to form a particulate containing web that may be laminated to other fabrics.
As noted above, particulate containing structures typically are laminated to other fabric layers to produce garments. One problem that has been encountered is that garments that contain particulate matter typically do not last for a suitable period of time. Washing and other stresses can result in delamination of the fabric layers, loss of particulate matter, and deterioration of the garment. The particulate matter often is adhered to the surfaces of the particulate containing structure that is laminated to various fabrics to form the garment. The particles interfere with bonding between fabric layers, whether bonding is accomplished by heat, pressure, adhesives, or some combination of these methods. Also, the particles are subject to abrasive removal, which reduces the effectiveness of the garment.
Filters containing particulate matter typically are not laminated to fabric layers, it being desirable to avoid restricting flow of liquids or gases through the filter so as not to increase pressure drop across the filter. For example, Shimomai et al. U.S. Pat. No. 3,998,988 discloses that filters may be prepared from finely divided adsorbent particles such as activated carbon adhered to a conjugate fiber of thermoplastic polymer composed of a higher melting component and a lower melting component. Fiber having a polyethylene core and a polystyrene sheath is specifically disclosed. The fiber is heated to bond the particles to the surface of the fiber without substantially adhering the fibers to one another. The fibers may be in the form of a nonwoven web of filaments or staple fibers, or a knit, woven, or nonwoven fabric having particulate matter adhered to the surface thereof. U.S. Pat. No. 3,998,988 does not recognize the problem of producing structures having particulate matter on the surface thereof and proposes no solution to the problem of having particulate matter on the surface of a web or fabric.
It would be desirable to produce open fibrous structures in which particulate matter may be immobilized within the fibrous structure between the surfaces thereof and does not interfere with bonding to other fibrous structures. It would also be desirable to produce a fibrous structure containing particulate matter that substantially is not subject to abrasion or abrasive removal of the particulate matter. Such open fibrous structures could be useful for filters and for laminating to fabrics for making garments or to other fibrous structures that do not as readily delaminate as prior garments or other structures.